The present invention relates to multilayer chip components such as multilayer chip beads or multilayer chip inductors, magnetic ferrite and multilayer ferrite components to be used to composite multilayer components represented by LC composite multilayer components, as well as a method for producing the same.
Multilayer chip ferrite components and composite multilayer components (called generically as xe2x80x9cmultilayer ferrite component or componentsxe2x80x9d in the present description) have been employed to various kinds of electric, electrical or electronic devices because of small volume and high reliability. The multilayer ferrite component is in general produced by laminating sheets or pastes for magnetic layers comprising magnetic ferrite and pastes for internal electrodes into a unitary one-body through a thick film laminating technique, sintering it, printing or transcribing pastes for external electrodes on the surface of the sintered body, and carrying out a sintering thereon. By the way, the sintering after laminating in one body is called as a co-firing. As a material for the internal electrode, Ag or Ag alloys are used because of low resistivity, and therefore as a magnetic ferrite material for composing magnetic layers, it is an absolute condition to enable the co-firing, in other words, enable the sintering at temperature below melting points of Ag or Ag alloys. Accordingly, for providing multilayer ferrite components of high density and high magnetic characteristics, it will be a key whether or not the magnetic ferrite can be sintered at the temperature below the melting points of Ag or Ag alloys.
NiCuZn ferrite is known as the magnetic ferrite which can be sintered at the temperature below the melting point of Ag or Ag alloys. In short, NiCuZn ferrite including powder of specific surface area rendered to be about 6 m2/g or more by a milling can be sintered at the temperature below the melting point of Ag (960xc2x0 C.), and it has broadly been used to multilayer ferrite components. However, since NiCuZn ferrite has the magnetic characteristic, particularly permeability xcexc which are sensitive to external stress or thermal shock (refer to, for example, xe2x80x9cPowder and Powder Metallurgyxe2x80x9d vol. 39 and 8, pp. 612 to 617 (1992)), problems arise as mentioned under during producing multilayer ferrite components. That is, the permeability xcexc is deteriorated by stress caused by barrel polishing and plating in a producing procedure, stress caused by difference in coefficients of linear expansion between the magnetic layers and the internal electrodes, and stress caused when mounting members on a base board, and inductance L is deviated from a designed value.
For solving the problems, two resolutions have been proposed. One of them is to face the magnetic layer and the internal electrodes to be opposite via a space therebetween (JP-A-4-65807). This proposal is to avoid the stress caused by the difference in the coefficients of the linear expansion between the magnetic layers and the internal electrodes. The other one is to cause Bi to exist in crystal grain boundaries of NiCuZn ferrite, thereby to generate tensile stress in crystal grains after sintering so as to make the sensitivity of the magnetic characteristic insensitive to the external stress (JP-A-10-223424). These two proposals were the effective measures for deterioration of the magnetic characteristic of NiCuZn ferrite against the stress.
However, NiCuZn ferrite will be naturally an expensive material, because NiO as a raw material therefor is at high cost. Having paid attentions to MgCuZn ferrite using MgO, Mg(OH)2 or MgCO3 which are cheaper than NiO, there have been made various improvements. For example, JP-A-10-324564 proposes an amount of B (boron) to be 2 to 70 ppm in MgCuZn ferrite.
However, MgCuZn ferrite of this publication is sintered at 1200xc2x0 C. according to examples, and it is difficult to apply this MgCuZn ferrite to the multilayer ferrite components directed by the invention. Because the co-firing cannot be carried out together with Ag or Ag alloys.
Japanese Patent No. 2,747,403 discloses the magnetic ferrite containing MgO, but does not refer to any sintering condition, and it is assumed not to satisfy the co-firing with Ag.
It is an object of the invention to offer magnetic ferrite of less deterioration of magnetic characteristic to stress, particularly of permeability xcexc, enabling the low temperature sintering, that is, to sinter at temperature below melting points of Ag or Ag alloys to be used as materials for electrodes, and multilayer ferrite components employing such magnetic ferrite. It is another object of the invention to offer a method of producing magnetic ferrite and multilayer ferrite components.
Powder for magnetic ferrite of the invention has the composition of Fe2O3: 40 to 51 mol %, CuO: 7 to 30 mol %, ZnO: 0.5 to 35 mol % and MgO: 5 to 35 mol %, in which a peak position of particle size distribution ranges 0.3 to 1.2 xcexcm. In powder for magnetic ferrite, one part of MgO may be replaced with NiO. Actually, a total amount of MgO and NiO is enough with 5 to 35 mol %.
Powder for magnetic ferrite of the invention has the composition of Fe2O3: 40 to 51 mol %, CuO: 7 to 30 mol %, ZnO: 0.5 to 35 mol % and MgO: 5 to 35 mol %, and is sintered at temperature below 940xc2x0 C. Depending on this magnetic ferrite, the sintering is available at temperature below 940xc2x0 C., and it is possible to obtain multilayer ferrite components of satisfied properties.
When the magnetic ferrite of the invention is sintered at temperature range of 940xc2x0 C. or lower, a shrinkage is 10% or higher. This fact shows that the sintering below 940xc2x0 C. is possible.
In the magnetic ferrite of the invention, the composition is desirable to be Fe2O3: 45 to 49.8 mol %, CuO: 8 to 25 mol %, ZnO: 15 to 25 mol % and MgO: 7 to 26 mol %.
The multilayer ferrite component of the invention uses the magnetic ferrite mentioned above and has external electrodes electrically connected to the internal electrodes which are alternately multilayer with the magnetic ferrite layer, said magnetic ferrite layer being composed of the sintered magnetic ferrite of Fe2O3: 40 to 51 mol %, CuO: 7 to 30 mol %, ZnO: 0.5 to 35 mol % and MgO: 5 to 35 mol % and also the internal electrodes being composed of Ag or Ag alloys.
The multilayer ferrite component of the invention has the alternate lamination of the dielectric layers and the internal electrodes, and may be integrally composed with the multilayer capacitor components having external electrodes electrically connected to the internal electrodes. In short, the composite multilayer components such as LC composite multilayer components are also defined as the multilayer ferrite components in the invention.
The multilayer ferrite component of the invention has the alternate lamination of the magnetic ferrite layers and the internal electrode layers and has external electrodes electrically connected to the internal electrodes, said magnetic ferrite layer being composed of the sintered ferrite of magnetostriction being 10xc3x9710xe2x88x926 or lower, and said internal electrode being composed of Ag or Ag alloys. In this multilayer ferrite components, it is preferable that the sintered ferrite is MgCuZn based ferrite having the composition of Fe2O3: 40 to 51 mol %, CuO: 5 to 30 mol %, ZnO: 0.5 to 35 mol % and MgO: 5 to 50 mol %.
The multilayer ferrite component of the invention is integrally united of inductor components having the alternate laminations of the magnetic ferrite layers and the internal electrode layers and capacitor components having the alternate laminations of the dielectric layers and the internal electrodes, and has the external electrode electrically connected to the internal electrode of the multilayer inductors and the multilayer capacitors. The magnetic ferrite layer of the multilayer inductor components is composed of the sintered MgCuZn based ferrite of the magnetostriction being 10xc3x9710xe2x88x926 or lower, and the internal electrode is composed of Ag or Ag alloys. In this multilayer ferrite components, it is preferable that the sintered MgCuZn based ferrite is MgCuZn based ferrite having the composition of Fe2O3: 45 to 49.8 mol %, CuO: 7 to 30 mol %, ZnO: 15 to 25 mol % and MgO: 5 to 35 mol %. Further, one part of MgO may be replaced with NiO. Actually, the composition has Fe2O3: 45 to 49.8 mol %, CuO: 7 to 30 mol %, ZnO: 15 to 25 mol % and MgO+NiO: 5 to 35 mol %.
The method of producing the magnetic ferrite comprises, according to the invention, a step of mixing raw powders, a step of pre-sintering the mixed raw powders at temperature of below 900xc2x0 C., a step of milling the pre-sintered material, a step of pressing into a desired with shape powders of a peak in the distribution being 0.3 to 1.2 xcexcm, selected from the milled powders, and a step of sintering the pressed bodies.
In the above magnetic ferrite producing method, the magnetic ferrite may be MgCuZn based ferrite where the raw powders are one or two or more of Mg, Mg(OH)2 and MgCO3, Fe2O3 powder, CuO powder and ZnO powder. In such a case, an addition amount of CuO powder is desirably 5 to 25 mol %.
The method of the invention of producing the multilayer ferrite components having the multilayer magnetic layers and internal electrodes, comprises mixing raw powders of the magnetic ferrite, pre-sintering the mixed raw powders at temperature of below 900xc2x0 C., milling the pre-sintered material, selecting such powders of a peak in the distribution of the particle size being 0.3 to 1.2 xcexcm from the milled powders, and subsequently comprises a step of making sheets or pastes for forming the magnetic layers with said powders of particle size distribution peak ranging 0.3 to 1.2 xcexcm, a step of alternately laminating said sheets or pastes and a material for internal electrodes for forming a multilayer body, and a step of sintering said multilayer body at temperature of 940xc2x0 C. or lower.
In the above multilayer ferrite producing method, the materials for the internal electrode may be Ag or Ag alloys. The sintering temperature is desirable at 870 to 930xc2x0 C.